ISO/TS 18621-21:2023

Graphic technology - Image quality evaluation methods for printed matter - Part 21: Measurement of 1D distortions of macroscopic uniformity utilizing scanning spectrophotometers

This document defines a measurement method for the evaluation of distortions in the macroscopic uniformity of printed areas that are oriented in the horizontal and vertical direction, such as streaks and bands. It provides requirements for the layout of the test form, the use of a colour measurement device taking measurements in a 2D sampling grid, and the formula to compute the Macro-Uniformity-Score. This document does not cover any non-adjacent or non-horizontal nor vertical patterns. Due to the used spatial frequency, the Macro-Uniformity-Score does not measure high frequency (fine) patterns such as missing nozzles.

Technologie graphique — Méthodes d’évaluation de la qualité d’image pour les imprimés — Partie 21: Mesure des distorsions 1D d'uniformité macroscopique à l'aide de spectrophotomètres à balayage

General Information

• Status: Published
• Publication Date: 26-Mar-2023
• ICS: 37.100.10 - Reproduction equipment
• Technical Committee: ISO/TC 130 - Graphic technology
• Drafting Committee: ISO/TC 130 - Graphic technology
• Current Stage: 6060 - International Standard published
• Start Date: 27-Mar-2023
• Due Date: 12-Jul-2023
• Completion Date: 27-Mar-2023

Relations

• Revises: ISO/TS 18621-21:2020 - Graphic technology - Image quality evaluation methods for printed matter - Part 21: Measurement of 1D distortions of macroscopic uniformity utilizing scanning spectrophotometers
• Effective Date: 06-Jun-2022

Overview - ISO/TS 18621-21:2023 (Graphic technology)

ISO/TS 18621-21:2023 defines a standardized, instrumented method to quantify 1D distortions in the macroscopic uniformity of printed areas (e.g., banding and streakiness) using scanning spectrophotometers. The method produces a single Macro‑Uniformity‑Score (0–100) based on averaged CIELAB measurements and adjacent CIEDE2000 colour differences along horizontal and vertical directions. The procedure is tailored for large, uniformly tinted areas and intentionally excludes non‑adjacent, diagonal or high‑frequency defects (for example, missing nozzles).

Key topics and technical requirements

• Test form and layout
  • Uniformly tinted area on an A4 test page with a minimum dimension of 156 mm.
  • Typical 2D sampling matrix assuming 6 mm pitch: ~31 × 26 patches (about 806 spots); perimeter patches may be omitted for processing.
• Measurement grid and device
  • Use a scanning spectrophotometer or a handheld device mounted on an XY table to capture a well‑defined 2D sampling grid.
  • Aperture diameter should be between 3 mm and 6 mm.
  • Maximum sampling pitch: 6 mm in both directions.
• Measurement conditions
  • Conform to ISO 13655; white backing per ISO 13655 Annex A.
  • Prefer M1 measurement condition and store results in ISO 28178‑compliant format when applicable.
• Computation and scoring
  • Average CIELAB values along rows and columns, compute adjacent CIEDE2000 differences, normalize and combine horizontal and vertical components.
  • Macro‑Uniformity‑Score is computed using a formula (includes fitted factors 40 and 15) and rounded to zero decimals; higher is better (100 = perfect uniformity).
• Reporting
  • Record test page dimensions, colour encoding, measurement condition/backing, any omitted perimeter patches, and final score.

Practical applications

• Objective evaluation of banding, streaks and large‑scale color non‑uniformity in digital, toner and inkjet printing systems.
• Quality control and acceptance testing in print production, OEM process validation, color laboratory benchmarking, and R&D for print engine development.
• Useful in process control when comparing printers, substrates or ink sets under defined test conditions.

Who should use this standard

• Print service providers, OEMs of printers and presses, color quality labs, prepress engineers, and researchers working on image quality metrics and print defect characterization.

Related standards

• ISO 13655 - Spectral measurement and colorimetric computation (measurement conformance).
• ISO/CIE 11664‑6 - CIEDE2000 colour‑difference definition.
• ISO 28178 - Data format for storing colorimetric measurements.
• ISO 12647‑7 - Reference point for proofing sampling (9‑point method comparison).

Keywords: ISO/TS 18621-21:2023, Macro-Uniformity-Score, macroscopic uniformity, scanning spectrophotometers, image quality evaluation, banding, streakiness, CIEDE2000, ISO 13655.

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 18621-21
Second edition
2023-03
Graphic technology — Image quality
evaluation methods for printed
matter —
Part 21:
Measurement of 1D distortions of
macroscopic uniformity utilizing
scanning spectrophotometers
Technologie graphique — Méthodes d’évaluation de la qualité
d’image pour les imprimés —
Partie 21: Mesure des distorsions 1D d'uniformité macroscopique à
l'aide de spectrophotomètres à balayage
Reference number
© ISO 2023
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Principles . 2
4.2 Apparatus . 3
4.2.1 General . 3
4.2.2 Measurement condition . 3
4.3 Procedure . 3
4.3.1 Test pattern . 3
4.3.2 Printing and measuring . 4
4.4 Evaluation . 4
4.5 Reporting . 5
Annex A (informative) Recommended tone value combinations . 6
Bibliography . 7
iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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different types of ISO documents should be noted. This document was drafted in accordance with the
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the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 130, Graphic technology.
This second edition cancels and replaces the first edition (ISO/TS 18621-21:2020), which has been
technically revised.
The main changes are as follows:
— Formulae (1) to (6) have been corrected;
— the Bibliography has been updated.
A list of all parts in the ISO 18621 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
The subject of image quality is broad and complex, due to its multidimensionality and the apparent
characteristics of human vision. Many different methods can be available to provide a measure of a
particular visual attribute in some particular viewing context and aimed at a particular printing
technology. It is a challenge to have image quality evaluation methods that are independent of the
marking technology, i.e. correlate with human perception to provide visual significance to measured
differences across many printing technologies. The evaluation of perceived image quality is an active
field of research.
The uniformity that can be achieved, or in fact the lack thereof, is an important factor in the evaluation
of the overall print quality. Uniformity refers to the subjective impression of the homogeneity of the
colour in extended areas up to the document size. Colour uniformity refers to all types of unintended
but visible variations in colour, that may go in any direction in colour space and may have any spatial
pattern. Spatial patterns include 1D, 2D, periodic, aperiodic, localized, large-scale and small-scale
variations. They can be identified as streaks or streakiness, banding, gradients, mottle, moiré and
others.
When evaluating perceived uniformity, the intended viewing distance should be taken into account. For
practical application it is also common practice to distinguish 2 categories of uniformity that depend on
the spatial frequency (or actually the angular frequency as seen by the eye):
— Microscopic uniformity such as graininess that is related to the imaging process and generally
consists of a 2D random noise pattern. It is visually relevant for image objects as small as few square
mm in size in case of normal reading distance (40 cm).
— Macroscopic uniformity involves distortions in the homogeneity that extend beyond few mm in one
or both geometric dimensions. It is generally visible across the document page size with examples
called banding, cording stripes or streaks.
This document focuses on the macroscopic uniformity that exhibits 1D type patterns that extend more
or less across the printed area of a page. It uses well established colour measurement instruments as
the basic measurement device, especially systems that can be combined with automated XY-tables for
performing well-defined measurements in a complete 2D grid of measurement locations in an easy
way. These systems generally have a minimum pitch in both dimensions of 6 mm. This method takes
a much more rigorous approach than the 9-point sample method that is defined in ISO 12647-7 that is
applicable to proofing systems.
The measurement method derives a single valued Macro-Uniformity-Score on a scale that ranges
from 100 (“perfect uniformity”) to 0 (“extremely poor uniformity”). It is based on the evaluation of
the average colour differences that occur in horizontal and vertical rows separately and adds them up
to arrive at a single value. Then a formula is applied to compute the Macro-Uniformity-Score that is
shown to correlate well with the perception of representative streaks or stripes of toner-based printing
systems as well as inkjet based systems.
This document describes a methodology in such a way that other documents can apply it for specific
use cases. Such documents will typically need to apply additional constraints on test pages and process
control in order to ensure that the resulting Macro-Uniformity-Score can be compared between
different printing devices, substrates and ink sets.
v
TECHNICAL SPECIFICATION ISO/TS 18621-21:2023(E)
Graphic technology — Image quality evaluation methods
for printed matter —
Part 21:
Measurement of 1D distortions of macroscopic uniformity
util
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